Initiated chemical vapor deposition (iCVD) can be used to deposit thin polymer films on a variety of substrates. In this work, the monomer precursor was introduced at an oblique angle to the substrate using an inlet extension, and the pattern of the resulting polymer film was studied as a function of deposition time, substrate temperature, monomer flow rate, reactor pressure, and vapor flow angle. The polymerizations of n-butyl acrylate, methacrylic acid, and 2-hydroxyethyl methacrylate were examined to determine the generality of the trends across several monomers. It was found that the monomer flow rate significantly affected the pattern of the deposited polymer by shifting the location of the thickest point in the films. Increasing the deposition time, decreasing the substrate temperature, and increasing the reactor pressure all increased the polymer deposition rate consistent with conventional iCVD; however, the pattern of the deposited polymer did not vary with these parameters. Computational analysis was used to determine how the inlet extension affects the pressure and velocity profiles within the reactor. The data demonstrate that the introduction of a monomer precursor at an oblique angle can be used to pattern polymer films during iCVD.

In this study, we applied oblique angle deposition to a modified initiated chemical vapor deposition (iCVD) process to synthesize porous poly(methacrylic acid) (PMAA) films. During the modified iCVD process, frozen monomer molecules are first captured on a cooled substrate, then polymerization occurs via a free radical polymerization mechanism, and finally, the excess monomer is sublimated, resulting in a porous polymer film. We found that delivering the monomer through an extension at an oblique angle resulted in porous films with three morphological regions. Region 1 is located nearest to the monomer extension outlet and consists of porous polymer pillars; region 2 consists of densified pillars, which occur due to the recapturing and polymerization of the sublimated monomer; and region 3 is located furthest from the monomer extension outlet and consists of dendritic structures, which occur due to low monomer concentration. We investigated the role of substrate temperature and monomer deposition time on the growth process. We found that changing the extension angle influenced the location of the regions and the film coverage across the substrate. Our results provide useful guidelines for tuning the structures within porous polymer films by varying the angle of monomer delivery.

This paper compares hazard and risk factors related to transporting hydrogen in natural gas pipelines. Properties of hydrogen-compressed natural gas (HCNG) blends and typical materials for the construction of transmission and distribution systems are evaluated to address the key properties that might impact hazard and risk factors. ASME (American Society of Mechanical Engineers) standards B31.8 and ASME B31.12 are reviewed for key differences applicable to HCNG blends. A methodology to identify compliance gaps and mitigate deficiencies if HCNG blends are transported in natural gas transportation systems is proposed.

In this study, a silicon-containing cross-linked polymer, poly­(1,3,5,7-tetravinyl-1,3,5,7-tetramethylcyclotetrasiloxane-co-ethylene glycol diacrylate) (p­(V4D4-co-EGDA)), was deposited onto high-viscosity silicone oil using initiated chemical vapor deposition (iCVD). The ratio of the feed flow rate of V4D4 to EGDA was systematically studied, and the chemical composition and morphology of the top and bottom surfaces of the films were analyzed. The films were microstructured, and the porosity and thickness of the films increased with increasing V4D4 content. The top of the film was composed of densely packed and loosely packed microstructured regions. X-ray photoelectron spectroscopy on the top and bottom surfaces of the films showed a heterogeneous chemical composition along the thickness of the film, with higher silicon content on the top surface compared to that on the bottom surface. To the best of our knowledge, this is the first study of iCVD deposition of a silicon-containing polymer film onto silicone oil. The results of this study can be used for the synthesis of polymer precursor films for the fabrication, via pyrolysis, of silicon-based inorganic membranes for use in hydrogen production using silicone oil to prevent infiltration of monomer into the underneath membrane support structure during vapor deposition.

Monomer precursor flow was introduced at an oblique angle to the substrate at two locations during the initiated chemical vapor deposition (iCVD) process using a branched nozzle inlet extension. The polymerization of methacrylic acid was systematically studied as a function of the nozzle length and the monomer flow rate. Our experimental data showed the evolution of two distinct symmetrical thickness profiles as the flow rate and nozzle length increased. The maximum thickness moved downstream along the axes of both nozzles as the flow rate and nozzle length increased. Computational models were used to study the effects of the nozzle length and the monomer flow rate on the velocity profile within the reactor. Increasing the monomer flow rate and the nozzle length resulted in increases in the velocity profile ranges and the movement of the location of the maximum velocity and local minimum velocity associated with the stagnation point. These velocity data provided insight for explaining the trends found in the experimental results. The data demonstrate the ability to use a branched nozzle inlet extension to control the location of polymer deposition during the iCVD process.